1. Field of the Invention
This invention generally relates to exhaust gas recirculation (EGR) valves of the type mounted in an exhaust gas recirculation system of an internal combustion engine. Such EGR valves are provided for the control of recirculation of exhaust gases, including uncombusted gases, discharged from the engine into the intake manifold. Such exhaust gas recirculation reduces the concentration of toxic waste gas in the exhaust gases, such as Nox gases. More particularly, the invention relates to an electrically actuated EGR valve which is operated by a step motor.
2. Related Art of the Invention
An example of a conventional EGR valve is disclosed in Japanese Utility Model Publication No. 53-88622 (1978). This publication discloses an EGR valve controlling the recirculation of exhaust gases in response to engine drive conditions of an internal combustion engine. This conventional EGR valve includes a signal chamber connected with an EGR port which generates a vacuum in response to the throttle valve opening degree. A diaphragm piston operates in response to the vacuum in the signal chamber and moves a valve which controls the exhaust recirculation gas passage. The rod of the valve and the rod of the diaphragm piston are integrally connected to one another. Thus, the conventional EGR valve controls the amount of exhaust gases through a diaphragm piston operated in response to a vacuum signal.
However, it is difficult for the conventional EGR valve to accurately and reliably control the amount of exhaust gases in response to engine drive conditions, and so inconsistent exhaust gas recirculation easily arises. Furthermore, the conventional EGR valve has a poor transient response characteristic on account of the time required to communicate a vacuum to a signal chamber from the EGR port.